Remove unused function export from binding

Removing it allows the Persistent<> to be removed, and the APIs around
persistents are more complex in v0.11. Also, removed unnecessary
`function(){...}();` wrapper around module (node does that itself).
Removed unused ObjectWrapper base from Syslog
Remove unused persistent callback to log()

log() allowed a callback to be passed as arg[3], but arg[2] was unused,
and the callback was never called (and not documented).
Support v0.10 through v0.11.13

The compatibility library is borrowed under ISC license from
bnoordhuis/node-heapdump.